This invention relates generally to semiconductor manufacture, and more particularly to an improved semiconductor card, and to a method and to a system for fabricating the card.
One type of electronic assembly containing semiconductor components is referred to as a xe2x80x9ccardxe2x80x9d. Examples of cards include multi media cards (MMC), memory cards, smart cards, and personal computer memory card international association (PCMCIA) cards. The present patent application refers to these types of cards as xe2x80x9csemiconductor cardsxe2x80x9d. These cards are also sometimes referred to as xe2x80x9cdaughter boardsxe2x80x9d.
Typically, the card includes a printed-circuit substrate (usually multilayer) that provides interconnection and power distribution for semiconductor components, such as semiconductor dice or packages, on the card. The card also provides interconnect capability to a next level package, such as a mother printed-circuit board. In addition to semiconductor components, the card can include other types of electronic components such as resistors, inductors and capacitors. Typically the components are mounted to a circuit side of the board, and the external contacts for the card are contained on an opposing back side of the substrate.
In the past it has been common practice to encapsulate the semiconductor components contained on the circuit side of the substrate using a xe2x80x9cglob topxe2x80x9d encapsulant. The cards typically also include a separate cover adhesively attached to the substrate, which encloses all of the components on the circuit side of the card. One shortcoming of this approach is that the cover can add thickness to the card. For most applications it is desirable to make the card as thin as possible. Also, the covers are typically fabricated separately, and then attached to the substrate using an adhesive. The cover represents a separate component which requires additional process steps, and which is subject to detachment from the substrate.
Besides being as thin as possible, another requirement for these cards is that the peripheral outlines and dimensions of the cards be as consistent as possible. A typical fabrication processes is performed on a strip which is similar to a lead frame and contains several printed circuit substrates. The individual cards are then separated from the strip using a singulation step such as sawing. Often the singulation step produces slivers, and roughened portions on the edges of the printed-circuit substrate. These defects can adversely affect the peripheral outline, dimensions and appearance of the card. Specifications on the peripheral outline and dimensions of cards, have been set by various industry standard setting bodies (e.g., PCMCIA). Defects such as slivers of substrate material, can make the peripheral outline of the card larger, such that the card does not meet the specifications.
The present invention is directed to a semiconductor card in which the components on the printed circuit substrate are encapsulated in a molded plastic body, such that the card can be made as thin as possible. In addition, the fabrication process employs a strip of substrate material, and a singulation step, designed to reduce defects, such as substrate slivers and dimensional irregularities.
In accordance with the present invention, an improved semiconductor card, and a method and a system for fabricating the card are provided.
The card includes a printed circuit substrate, which comprises an electrically insulating material, such as an organic polymer resin reinforced with glass fibers. The substrate includes a circuit side with a pattern of conductors thereon, a back side with a pattern of external contacts thereon, and a plurality of interlevel conductors which electrically connect the conductors on the circuit side to the external contacts on the back side. The substrate is initially a segment of a strip containing multiple substrates. The strip is similar in function to a semiconductor lead frame, and allows various fabrication processes to be performed on several substrates at the same time. The substrate is connected to the strip with connecting segments that are similar in function to tie bars on a semiconductor lead frame. In addition, a peripheral outline of the substrate is defined by a peripheral opening in the strip.
The card also includes one or more semiconductor components mounted to the circuit side of the substrate in electrical communication with the conductors on the circuit side. The semiconductor components can comprise bare dice wire bonded to the conductors, bumped dice flip chip mounted to the conductors, or semiconductor packages bonded to the conductors. The card also includes a molded encapsulant on the circuit side of the substrate which encapsulates the components. The card also includes a molded plastic body which covers the encapsulant, the remainder of the circuit side, and the edges of the substrate.
The plastic body includes one or more notches formed on edge portions thereof in alignment with the connecting segments for the substrate. Although most portions of the connecting segments are removed during singulation of the substrate from the strip, some portions of the connecting segments (e.g., slivers) can remain in the notches following the singulation step. However, because the notches are configured to enclose these remaining portions of the connecting segments, the peripheral outline and dimensions of the card can still meet specification. The notches in addition to enclosing defects on the substrate also function to provide access to the connecting segments for singulating the substrate from the strip.
A method for fabricating the semiconductor card includes the initial step of providing the strip containing multiple printed circuit substrates. The peripheral outline of each substrate on the strip is defined by the peripheral openings through the strip, and each substrate is connected to the strip by the connecting segments. In addition, the method includes the steps of mounting the semiconductor components to the substrates on the strip, and then encapsulating the semiconductor components.
Following the encapsulating step, a molding step is performed to mold the plastic bodies to the substrates on the strip. The molding step can be performed using a molding apparatus having mold cavities configured to mold the plastic bodies to the strips. The mold cavities include pins configured to contact the connecting segments for the substrates, and to form the notches in the plastic bodies in alignment with the connecting segments. Following the molding, a singulation step is performed by severing the connecting segments to separate the substrates from the strip. During the singulation step, the notches provide access for severing the connecting segments. In addition, any slivers from the connecting segments remain in the molded notches such that the peripheral outline of the card meets specification.
A system for performing the method includes the strip containing multiple printed circuit substrates connected to the strip by the connecting segments and defined by the peripheral openings in the panel. In addition, the system includes the molding apparatus having the mold cavities for molding the plastic bodies to the substrates. The system also includes the pins in the molding cavities configured to mold the notches into the plastic bodies and to hold the connecting segments down during the molding step. The system also includes a punch apparatus having cutters configured to move through the notches in the plastic bodies to sever the connecting segments.